1. Field of the Invention
The present invention relates to the oil and gas industry. More particularly, the present invention relates to active structural health monitoring of marine composite riser systems in a production phase.
2. Description of Related Art
In the oil and gas industry, a riser is a string of pipe between the surface and sea bottom. Oil and gas riser pipe strings are assembled sequentially and connect a surface ship, rig, or platform to subsea equipment, including, for example, a Christmas tree, blow out preventer (BOP), or lower marine riser package (LMRP), as understood by those skilled in the art.
During a typical field installation at sea, marine riser pipes are individually lifted from the deck of a vessel, connected to each other at the riser spider, and run down. Two riser pipes are joined, or coupled, by means of a mechanical connector. The length between two riser couplings varies typically between 40 to 80 feet depending on the requirements for the riser system.
Riser Lifecycle Management Systems (RLMS) have been described, such as in co-owned U.S. patent application Ser. No. 12/029,376, which is herein incorporated by reference in its entirety. Such riser lifecycle management systems, for example, can provide asset managers a list of all the riser assets allocated to specific vessels and provide a further breakdown of those assets that are currently deployed, are on deck, or are out for maintenance, along with the expected return date; a list of upcoming scheduled maintenance events; an estimate of the amount of operational life being expanded by a particular riser asset; and an estimate of the total amount of operational life used by a particular riser asset, along with the details of the most damaging events (i.e., a certain hurricane event).
Piezoelectricity is the generation of electricity or of electric polarity in dielectric crystals subjected to mechanical strain and stress, or the generation of strain and stress in such crystals subjected to an applied voltage.
Existing structural health monitoring approaches and techniques all have various advantages, disadvantages, and trade-offs.
X-ray radiography, for example, is capable of internal damage and propagation detection, is relatively simple, and can produce a permanent record of results (i.e., an x-ray image). X-ray radiography is, however, expensive to implement, requires expensive equipment, is time-consuming, and requires skills for correct interpretation. As such, x-ray radiography is not fully automated (i.e., human operators are required).
Strain gauges, for example, offer light-weight and low-power operations for structural health monitoring. Strain gauges are portable, can be surface mounted, and provide a relatively simple procedure. Strain gauges are, however, expensive to implement and require expensive equipment.
Optical fibers, for example, are generally a light-weight solution that can cover large areas utilizing inexpensive equipment for structural health monitoring. Optical fibers, however, are expensive to implement, requiring laser in the diagnostic process; optical fibers must be embedded in the structural health monitoring solution.
Ultrasonic structural health monitoring solutions, for example, are portable and sensitive to small damage; they offer a quick scan of a large area. Ultrasonic structural health monitoring solutions, however, utilize very expensive equipment, provide complex results, and require specialized systems for operation.